Smid, 23, set career highs in assists and points with 11 last season. He had no goals and 57 penalty minutes in 60 games.
"I'm very pleased to have Ladislav signed," Oilers general manager Steve Tambellini said in a statement. "He's a very competitive young defenseman that has the ability to contribute in all situations."
Smid has played in 202 career NHL games, all with the Oilers, recording three goals, 22 assists and 152 penalty minutes.
"This is great news for me," Smid said. "I really enjoy playing for the Oilers. I feel my game is improving every year and I can't wait to get started again this fall."
Brule, 22, split last season between the Springfield Falcons of the American Hockey League and the Oilers. He had two goals and one assist in 11 games for Edmonton, and 13 goals with 11 assists in 39 games for Springfield.